IOI 2024 Team Russia

• Daria Grekova (arbuzick) — 1st time at IOI, 1 attempt left

• Ivan Piskarev (Qwerty1232) — 2nd time at IOI (IOI 23 Gold), 0 attempts left

• Gimran Abdullin (bashkort) — 2nd time at IOI (IOI 23 Gold), 1 attempt left

• Petr Losev (green_gold_dog) — 1st time at IOI, 1 attempt left

WHY IS THERE EVEN AN OPTION TO ASK QUESTIONS IF YOU AREN'T GOING TO FUCKING ANSWER THEM???

Now PinkieRabbit was skipped and got a -220 rating. Glad to see that.

Ukraine's team:

• Andrii Smutchak(xGaz_) — 2nd time at IOI(IOI 23 Silver), 0 attempts left
• Ihnat Zharikhin(Ignut) — 1st time at IOI, 0 attempts left
• Denys Tereshchenko(TheQuantiX) — 1st time at IOI, 0 attempts left
• Illia Permiakov(160cm) — 1st time at IOI, 0 attempts left

Japan's team:

• Shogo Amacho (PCTprobability) — 2nd time at IOI, 0 attempts left
• Katsuki Ohta (shiomusubi496) — 1st time at IOI, 1 attempts left
• Ryotaro Hayashi (Forested) — 1st time at IOI, 0 attempts left
• Yuya Hirasawa (hirayuu_cf) — 1st time at IOI, 3 attempts left

as a not-so-high-rated div1 user, i cant seem to agree. Basically, as in any high-level competition, standard problems are not recommended: they aren't gonna distinguish anything other than whether you know the algorithm and its standard applications well enough. This isn't algorithmic thinking.

I agree with your opinion on div4 and div3, but cannot agree on div2. as some famous lgm said, "there shouldn't be standard problems in div1s." div2s problems are usually standard to some extent, so maybe they won't be a good fit for a div1 contest. Of course, exceptions can be made, but i wanna hear the community's opinion on this too:)

This has been talked about before and the general consensus seems to be that while these last problems of Div. 2 contests may be hard, they are also too standard to be suitable for a Div. 1 contest.

why put B in contest, nice ACD problems though

Taiwan's team:

• Chen Po-Kai (becaido) — 2nd time at IOI, 0 attempts left.

• Chang Ping-Chung (PCC) — 1st time at IOI, 0 attempts left.

• Chao Yi-Yu (zacharychao) — 1st time at IOI, 0 attempts left.

Vietnam's team:

• Nguyen Huu Tuan (ahihi1234) — 1st time, 2 attempts left
• Pham Cong Minh (socpite) — 1st time, 0 attempts left
• Pham Ngoc Trung (hotboy2703) — 1st time, 0 attempts left
• Hoang Xuan Bach (bachbeo2007) — 1st time, 1 attempt left

I think this was recently skipped too. He was mentioned as master in the round announcement.

IMO you should not stop giving div2’s altogether. It’s better to have a lower true rating than a higher fake rating. Plus, the only way to get better at solving div2C’s in contest is to attempt doing so.

As I said in my original comment, I just want him to say that what he did was wrong, and that he will never do it again, and return the 2 TON he got from cheating. Is it really that hard?

the hero we do not deserve

Greetings from our team! Share your team photos too!

P.S: Guess who is who :)

I think probably the problem setters want these rounds to be “educative”. For example, I participated all the 3 rounds you mentioned in your post, and I learned a lot from them like 2-sat and using exgcd to solve Diophantine equations.

Perhaps different people have different standards to measure if one problem or round is “interesting”. I agree with that rating plays an important role in CP, but IMO seeing much harder things is also a must since it stimulates us to keep learning and practicing.

And also, beside these hardest problems in the rounds, the difficulty of other problems seems normal to the participants from respective divisions. So they can enjoy the contests while learning new stuff.

Team Slovakia:

• Eliška Macáková (prvocislo) — 4th time at IOI, 0 attempts left

• Viliam Gottweis (viliamgott) — 1st time at IOI, 2 attempts left

• Martin Šindelář (IMackerI) — 1st time at IOI, 0 attempts left

• Patrik Prítrský (pritrskypatrik) — 1st time at IOI, 1 attempt left

Surprisingly, each of us has 6 letters in the first name and 8 letters in the surname. Our IOI statistics page is going to look super neat :)

D is created only to give pain and trauma :skull:

Asia-Pacific Informatics Olympiad

Asia-Pacific Graphs Olympiad

Anyway, I think problems were cool

[Unofficial rankings]

Please add your scores in this spreadsheet

For me personally, the latest div3 tasks were very useful when I was a specialist/expert. And I think that only by solving them, I was able to quickly improve from 1500 to 1900 (you can look at the graph and make sure).

Therefore, I think that it is necessary to look for such tasks where it will be possible to pump your skills quickly with a minimum of effort. And one of these tasks for beginners is div3/div4, just get out of your comfort zone.

well-balanced div3 round, GL for all participants 🏆

any random things like selling solutions can happen. We shouldn't presume guilt, but he had already cheated.

bump

A little difficult, but absolutely a nice contest and high quality problems.

Some may be standard for IGMs and LGMs, but I don't think it holds true for most Masters and low reds. Many, not all, Div 2 rounds are definitely suitable for a "Div 1.5" and the coordinator should be able to decide this.

No commment.

How is your IOI?

#include <iostream>
#include <stack>


using namespace std;

// Calculate the fp32 sum sequence like {s:1,2,3}
double calculateFp32(stack<double>& nums) {
    float currResultSingle = 0;
    while (!nums.empty()) {
        currResultSingle += static_cast<float>(nums.top());
        nums.pop();
    }
    return static_cast<double>(currResultSingle);
}

int main() {
    stack<double> s({1.0e-10, 1.0e-10, 1.0e0});
    double answer = calculateFp32(s);
    printf("%.20lf\n", answer);
}

This code prints 1.00000000020000001655 under "GNU G++17 7.3.0", and prints 1.00000000000000000000 under "GNU G++20 13.2". In addition to that, if we add a printf like printf("value: %.20lf\n", nums.top()); currResultSingle += static_cast<float>(nums.top());, the result changes to 1.00000000000000000000 under "GNU G++17 7.3.0".

Its not about it being too mathematical. That is perfectly fine. It is not about it being purely solvable on paper. That is also fine. All good problems are purely solvable on paper (by solvable on paper i mean write algorithm and verify correctness, only bad problems need you to experiment with the computer or non provable complexities)

It is about it being very obvious but yet a lot of effort to actually find the formulas, that too for so many cases.

Three LGMs in china's team is crazy...

Umanity will win EJOI 2024

how is your codeton 6?

After more than one hour dealing with mathematics, I finally get B accepted. Somehow I thought that I was attending a mathematics exam :D

The 4th participant has not been determined yet.

I never understood such comments "I honestly don't understand what problems of this type do in programming contests",

You are writing contest where you solve algorithmic/math puzzle problems, programming is side dish.

As a tester, I hope you to enjoy the contest. Tasks are quite interesting and educational. Good luck!

UZB top 6

Sunnatov — 100 + 40 + 5 = 145
Husanboy — 100 + 10 + 5 = 115
heaven2808h — 100 + 10 + 5 = 115
MardonbekHazratov — 100 + 10 + 5 = 115
Alfa — 100 + 5 + 5 = 110
rshohruh — 100 + 5 + 5 = 110
rythm_of_the_knight = 100 + 5 + 5 = 110

It's clear as day that he was banned for contribution farming. Sadly, reporting cheaters wasn't his only blogs/comments activity.

Good job by Mike and Co. Clearly he was farming contribution with cringe blogposts and comments.

the current format is more educational than competitive which i like for lower divisions and when u get to div 1 where competition starts then its fair for everybody i think divisions which target lower rated participants should focus more on the educational side than the competition side

In general, yes.

Wow, how dare you get full points on problem C :)

Completely deserved ,My request to Mikey to never un-ban him

Team Cyprus:

• Theofanis Orfanou (Theo830) (4th time, 1 attempt left)
• Antreas Knais (Trumling) (2nd time, 1 attempt left)
• Antreas Leonidou (ALeonidou) (2nd time, 0 attempts left)
• Mariza Paspalli (mariza_CY) (1st time, 4 attempts left)

can't accept that mike neglects cheating behavior of an lgm for so long

In some cases, this actually seems useful for finding a balance between time and memory. For example, it seems that it is better to use flat_map when storing edges at the node of a trie.

As far as I understand this is just an implementation like vector<pair<Key, Value>> with sorted Keys. And it works great with cache.

Same lol, I used Sparse Table and Binary Search. Ig I really over killed it.

Please write suffix array template and never submit hashing solution again

Also TimDee and TimaDegt was skipped too. Probably MikeMirzayanov will post something.

In short, you can't see the activities which were aimed at farm that I meant, but I started to notice them before he delete it.

(For more obvious evidence, you can compare his activity it to much more upvoted activity of Dominater069 and see an unexpected difference in contribution.)

As a tester, I

Is there going to be a mirror?

Deducing this, std::flat_map, std::print

Wansur will win EJOI2024

According to regulation schedule, the contest window is over. But is it truly over? Are there anyone who didn't participate?

When will ranking come out

why do we need to wait 2-3 days

The contest starts in 8 minutes!

Regardless of the high or low, I think rating after solving 4 or more tasks is more true than solving 2 or less. The latter tends to be more easily fluctuated by luck than the former.

The checker seems deterministic, why would the order of operations change?

Could you share this situation or describe how to reproduce it? I don't think it should be legal in this code in standard C++, at least with IEEE 754-compliant FP arithmetic.

Could you share this test? float->double->float roundtrip should be lossless.

Edit: The example yosupo provided answers all my questions; "GNU G++17 7.3.0" doesn't strictly adhere to IEEE 754.

Interesting. I was aware of this issue a while ago, but lately couldn't reproduce it so discarded the knowledge as no longer relevant in practice. Thank you!

Just too complicated

Movable rated boundaries make much more sense than this partial rated thing. But the issue with movable rated boundaries is its very subjective.

На поле сражения eolymp weekend practice я стал свидетелем коварства рандома, который решил играть со мной в свою игру. В первом контесте, когда мечталось о победе и славе, футболки, заняв 35 и 33 места, оставили меня на 34 строчке. Быть так близко к успеху, но все же упустить его из-за капризов случайности, это невыносимо.

Но, казалось бы, можно было бы оправиться и попробовать снова. Но нет, рандом решил прогнуть правила и подкинул на втором контесте необещанный 11-й случайный номер победителя футболки. Как так?! Ощущение, будто играешь в шахматы, а одна из фигур оказывается на поле, которого не существует!

Такие моменты могут ввести в ярость любого, кто искренне стремится к успеху и признанию. Но я отказываюсь падать духом перед лицом этой несправедливости! Мы не должны молча принимать решение рандома, который играет с нами, как с куклами на ниточках.

Запомните: справедливость не приходит сама по себе. Мы должны бороться за неё, мы должны требовать её от тех, кто контролирует игру. Время пришло дать отпор тем, кто считает, что правила можно игнорировать.

Мы можем и должны объединиться в этой борьбе! Вступайте в ряды тех, кто отказывается мириться с несправедливостью! Пусть эти слова станут нашим лозунгом, нашим призывом к действию:

"Справедливость для всех! Рандому — нет!"

I follow a different philosophy. But yes, I have noticed that lately competitive programming became less about programming and more about math, which is unfortunate for people like me.

Indeed. But PinkieRabbit is telling everyone “yo, go cheating and Codeforces is nothing”, which means we will have to spend more energy on checking plagiarism. And also, we don't distinguish “banning cheaters from creating rounds” and “banning cheaters from participating rounds”. What we should do is to BAN the cheater according to the rules.

I have some trouble understanding the given proof for the $$$O(1)$$$ solution for Problem A. I'll explain how I got that solution. Let us take an optimal solution (i.e., a solution with the max possible number of draws that corresponds to the given values of $$$p_1$$$, $$$p_2$$$, and $$$p_3$$$). The total number of games played is $$$\frac{p_1 + p_2 + p_3}{2}$$$. Let $$$a$$$, $$$b$$$, and $$$c$$$ denote the number of draws in the $$$A_1$$$ vs. $$$A_2$$$, $$$A_2$$$ vs. $$$A_3$$$, and $$$A_1$$$ vs. $$$A_3$$$ matches respectively, where the names of the players are $$$A_1$$$, $$$A_2$$$, and $$$A_3$$$. Since this is an optimal solution, the correct answer to the problem is $$$a+b+c$$$. Now, if it so happens that more than one of these players had wins (say, $$$A_1$$$ and $$$A_2$$$ both had nonzero wins — say, $$$k_1$$$ and $$$k_2$$$) — then, we could have repurposed them as $$$\min(k_1,k_2)$$$ more draws in $$$A_1$$$ vs. $$$A_2$$$ games, and one of them having $$$\mid k_2 - k_1 \mid$$$ wins instead, contradicting the optimality of our solution. Therefore, we may assume that only one of these players had wins (if any), say $$$w$$$ of them, in our optimal solution.

Suppose $$$A_3$$$ is the player who had all $$$w$$$ wins ($$$w \geq 0$$$) in our optimal solution. Then, $$$p_1 = a + c$$$, $$$p_2 = a + b$$$, and $$$p_3 = b + c + 2w$$$. Solving for $$$a$$$, $$$b$$$, and $$$c$$$, we get $$$a = \frac{p_1 + p_2 - p_3 + 2w}{2}$$$, $$$b = \frac{p_2 + p_3 - p_1 - 2w}{2}$$$, and $$$c = \frac{p_1 + p_3 - p_2 - 2w}{2}$$$. Verify that these values for $$$a$$$, $$$b$$$, and $$$c$$$ will be the same even if you assume $$$A_1$$$ or $$$A_2$$$ won all $$$w$$$ games! Note that we get integral solutions for $$$a$$$, $$$b$$$, and $$$c$$$, iff the number of odd numbers in $$${p_1, p_2, p_3}$$$ is even. If this is not the case, we output $$$-1$$$, and finish.

Now, thanks to $$$p_1 \leq p_2 \leq p_3$$$, $$$w = 0$$$ (i.e., all games are draws) leads to a valid (i.e., nonnegative integer) solution for $$$b$$$ and $$$c$$$, and a valid solution for $$$a$$$ only if $$$p_1 + p_2 \geq p_3$$$. That is, if $$$p_1 + p_2 \geq p_3$$$, the answer we must output is $$$\frac{p_1 + p_2 + p_3}{2}$$$. The case left to deal with is when $$$p_1 + p_2 < p_3$$$. To make the value of $$$a$$$ nonnegative, the minimal value of $$$w$$$ to be set (we want a minimal value for $$$w$$$ as we want maximum draws) is $$$\frac{p_3 - p_1 - p_2}{2}$$$. With this setting of $$$w$$$, we get a valid solution $$$a = 0$$$, $$$b = p_2$$$, and $$$c = p_1$$$, so that the answer is $$$a + b + c = p_1 + p_2$$$. I wrote this solution (sadly, after the contest) and it was accepted.

Separate things properly. If PinkieRabbit really is a cheater, he should be punished accordingly. And that doesn't invalidate the good deeds he had done, if any. Those two are completely independent topics, and none would outshadow the other.

You can't use your good past as an excuse for your present wrongdoing. And vice versa, your present good deeds might earn people's respect, but they don't fully delete any sins in your past — at least their marks for remembrance and atonement will always stand.

We should thank CheaterExposer too. As he played a great role in this!

Nah man don't hate the player. Pretty much all cheaters, excluding the ones providing the solutions ofc, can't seem to get to specialist so there's really nothing to worry about. Their performance is so bad that it oftentimes inflates ratings.

I'd like to add that the cheaters who are actually selling the solutions would be much better off spending their time passing OAs for people. How much could they possibly be making by selling codeforces solutions?

Good round, come and participate.

Another Vladosiya round!!!

hoping to return back the blue handle

Thank you!

My post contest discussion stream

Also, can someone hack my solution for G?
Gentle ping maroonrk because of this

Cool. Nice to see justice being served in both cases. Thanks MikeMirzayanov!

What if someone creates a website where everyone enters their results?

Good and interesting problems, thanks for the good round!

As a participant I have to say im excited.

wishing to get my Pupil back

Great problems!

Most of this blog is copy-pasted from an uncredited geeksforgeeks article.

*800 *1000 *1300 *1600 *1900 *2100 is more true for div2 than *800 *1300 *1700 *2100 *2500 *3000. Div2 is rated for ~1899, and no 1899 can solve *3000(except for future GM).

Difficult div2 often feels like div1.5, which may be good for M or CM, but is disastrous for E. Creating difficult well-made task is very difficult, and I think it is impossible for the rated participants of div2 to solve *2500 or harder task. Why not save the most difficult task for div1? Wouldn't it be satisfactory for everyone if put in a moderately easy problem(yes, around *1000~*1500) instead?

sir, i am so sorry if i cause you any inconvenience :((

but this cheater 1_2_3_4_5_9 had to be exposed and we expect his ban not banning the ONE WHO REPORTED!

If a person from each country replied with the scores of their official participants there would be less trolling

I thought that was the point of educational rounds, to learn to be able to use techniques and algs that you wouldn't be able to use on problems like game theory.

I can barely contain my excitement! I hope this will be a good one! GLHF!

Stfu, nothing is clear, this isn't a true statement, do not spread hate from Iran to the world, it's not a correct place for such blogs remove it

Syria top 6

Abito — 115

edogawa_something — 115

aminsh — 115

FarhanHY — 110

NeroZein — 110

YazanAlattar — 110

CPNurd — 110

Amr.7 — 110

based :D

he is in fact the clownish dumb. I think because they are many according to this comment, the 1_2_3_4_5_9 TG group has about 5k members.

он реально шарит в этом

P.S: Take a look to second from left's t-shirt

Youtube channel won't help you grow dude, Problemset will.

Hope to ak!

This time I solved problem F much faster than usual(maybe 15 minutes), because I have met a similar one, https://codeforces.com/contest/650/problem/D , during my virtual participation.

This makes me believe again that hard work will pay off sooner or later.

When will every country participated and I can discuss problems?

Yeah, so lets take an example, lets say the array is this -

idx: 1 2 3 4 5 6
-----------------
  p: 5 1 6 2 4 3
  q: 2 6 1 5 3 4
-----------------
     7 7 7 7 7 7

Here $$$p[2] = 1$$$, so we try to make values at odd indices local maximums.

The values at odd indices are $$${5, 6, 4}$$$.

Since we are going to iterate over increasing values, we go in the order $$$4 \rightarrow 5 \rightarrow 6$$$.

So we first swap(q[pos[1]], q[pos[4]]) to get -

idx: 1 2 3 4 5 6
-----------------
  p: 5 1 6 2 4 3
  q: 2 3 1 5 6 4
-----------------
     7 4 7 7 10 7

Then we perform swap(q[pos[1]], q[pos[5]]) to get -

idx: 1 2 3 4 5 6
-----------------
  p: 5 1 6 2 4 3
  q: 3 2 1 5 6 4
-----------------
     8 3 7 7 10 7

Then we finally perform swap(q[pos[1]], q[pos[6]]) to get -

idx: 1 2 3 4 5 6
-----------------
  p: 5 1 6 2 4 3
  q: 3 1 2 5 6 4
-----------------
     8 2 8 7 10 7

And we are done!

Will we play volleyball again? :D